buttonpower supplyswitches
I have a project that uses a computer case and PSU, but not motherboard, to turn on the PSU, all we know is to put green cable to GND.
The problem is the ON Button, it's momentary and I need to keep the PSU on. I've seen some circuits with arduino but because the price its not an option (50 USD arduino).
Any ideas?
This is variation on my answer to this question. Like Mike, I am also using a P-channel MOSFET. The OP stated: "The Voltage regulator requires Vin +/- 0.3V on the Enable Pin", and "MicroController Output Pin High state is 2.7V Max". Therefore when the battery voltage is above 2.7v, the µC will be unable to supply the required voltage to meet the voltage spec for the Enable lead. So I am using the control lead of the µC to control the MOSFET, which in turn switches the battery voltage (or Vin) to the Enable lead.
Initially, the control lead from the µC is configured as an input. When the button is pressed, battery power is applied through a Schottky diode (keep Vf below 0.3v) to enable the regulator. The µC then configures the control lead as an output and grounds it, keeping the enable lead high through the MOSFET (which keeps the voltage at the battery level). Meanwhile, the button can be used as an input.
The circuit should draw very little power (less than 1 µA) when the µC is powered down, assuming the regulator shuts down completely when the Enable lead is low.
This eliminates the cost of the LTC2954 chip which runs over $2 in 500 unit quantities. This circuit should be under 10 cents in quantity (except for the switch and regulator).
Believe it or not, that black lump is epoxy covering an integrated circuit, probably a small microprocessor. These are often caseless chips, just the IC die glued to the PCB with fine wires between the pads on the chip and PCB.
Many microcontrollers can be put into a deep-sleep state where they draw just a few microamps, so little so as not to significantly affect battery life. They spend all of their time in deep sleep until someone presses the button, which is connected to an interrupt line to wake it up.
Best Answer
The power control line for your power supply requires a maintained contact to ground to remain powered.
There are a few options that you can use.
1) Use a toggle switch or latching push-button switch.
2) Use an alternate-action latching circuit to convert the momentary signal from your switch to a latching signal.
If your momentary switch is floating, there is a simple circuit that works well. What I mean by "floating" is that both sides of the switch are completely isolated.
The reason I mention this is because sometimes, you need one side of the switch to be connected somewhere else, such as ground.
simulate this circuit – Schematic created using CircuitLab
This is a classic 2-inverter alternate-action latch that I first saw in Don Lancaster's "CMOS Cookbook" back in the '70s. It works extremely well and can be very tiny - some of the new "Tiny Gate" logic contains both inverters in a single 6-pin package.
My only changes to Don's circuit as published is to add an extra RC filter to the first inverter. This has two benefits:
1) Reduces the possibility that impulse noise (static discharge, etc) can change the state of the latch when not desired.
2) Provides a defined output logic state when the circuit powers up. You can connect C2 to Ground if you want the latch to power up with the output LO or have it tied to the V+ rail as I have shown if you want the latch to come up with the output HI.
I assume that you want the power supply to remain OFF when connected to the AC mains, so I have shown the latch to power up that way.
The chip needs to be powered from the 5V standby power lead from the supply.